Grinding machine and grinding method

ABSTRACT

A grinding machine includes a wheel spindle stock in which a wheel spindle is rotatably provided. The wheel spindle moves between first and second spindles so that a third rotation axis of the wheel spindle moves in the direction perpendicular to first and second rotation axes on an XZ plane extending through the first and second rotation axes. The grinding wheel that is held by the wheel spindle grinds a first workpiece as the wheel spindle stock moves toward a first headstock, and grinds a second workpiece as the wheel spindle stock moves toward a second headstock.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2014-238298 filed on Nov. 26, 2014 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to grinding machines that grind a workpiece and grinding methods.

2. Description of the Related Art

For example, Japanese Patent Application Publication No. 2011-189433 (JP 2011-189433 A) describes a grinding machine that includes a plurality of pairs of workpiece holding portions along the outer peripheral edge of a rotary table and grinds pairs of workpieces with two grinding wheels having different shapes in order to improve grinding efficiency.

The configuration of the grinding machine described in JP 2011-189433 A uses a grinding moving mechanism in addition to an inter-spindle moving mechanism. When grinding a workpiece, the inter-spindle moving mechanism moves a wheel spindle stock between the pair of workpieces (in the horizontal direction in FIG. 3), and the grinding moving mechanism moves the wheel spindle stock in the grinding direction (in the vertical direction in FIG. 4). Since this grinding machine has a large number of moving axes, the device configuration and machining control are complicated, which tends to increase cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a grinding machine having a simple device configuration and a grinding method in which machining can be easily controlled.

According to one aspect of the present invention, a grinding machine includes: a first headstock having a first spindle that can rotate about a first rotation axis extending in a vertical direction and that rotatably supports a first workpiece; a second headstock having a second spindle that can rotate about a second rotation axis separated from the first rotation axis at a predetermined interval and extending parallel to the first rotation axis, and that rotatably supports a second workpiece different from the first workpiece; a wheel spindle stock that has a third rotation axis extending parallel to the first and second rotation axes and that moves between the first and second headstocks so that the third rotation axis moves in a direction perpendicular to the first and second rotation axes on a plane extending through the first and second rotation axes; a wheel spindle that is rotatably provided in the wheel spindle stock; and a grinding wheel that is provided on the wheel spindle, that grinds the first workpiece as the wheel spindle stock moves toward the first headstock, and that grinds the second workpiece as the wheel spindle stock moves toward the second headstock.

In the grinding machine of the above aspect, a direction in which the grinding wheel moves between the first and second headstocks is the same as that in which the grinding wheel grinds the first and second workpieces supported on the first and second spindles of the first and second headstocks when grinding the first and second workpieces. This eliminates the need for a grinding moving mechanism separate from an inter-spindle moving mechanism, which simplifies the device configuration and reduces facility cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1A is a perspective view of a grinding machine according to an embodiment of the present invention;

FIG. 1B is a front view of the grinding machine of the embodiment;

FIG. 1C is a top view of the grinding machine of the embodiment;

FIG. 1D is a top view of the grinding machine of the embodiment with a wheel spindle of FIG. 1C removed to expose to a portion near a grinding wheel;

FIG. 1E is a block diagram of a control device of the grinding machine of the embodiment;

FIG. 2 is a timing chart showing the operation sequence of the grinding machine;

FIG. 3A is a diagram showing the operation that is performed when a workpiece is picked up from a conveyor in a load/unload device;

FIG. 3B is a diagram showing the operation that is performed when a workpiece is picked up from a first spindle in the load/unload device;

FIG. 3C is a diagram showing the operation that is performed when a workpiece is set onto the first spindle in the load/unload device;

FIG. 3D is a diagram showing the operation that is performed when a workpiece is set onto the conveyor in the load/unload device;

FIG. 4A is a diagram showing the state where the grinding wheel has been positioned at an initial position;

FIG. 4B is a diagram showing the state where the grinding wheel has been positioned at a grinding start position when a workpiece on the first spindle is to be ground;

FIG. 4C is a diagram showing the state where the workpiece on the first spindle is being ground;

FIG. 4D is a diagram showing the state where the grinding wheel has been positioned at a grinding start position when a workpiece on a second spindle is to be ground;

FIG. 4E is a diagram showing the state where the workpiece on the second spindle is being ground;

FIG. 5A is a diagram showing the state where a truing device has been positioned at a standby position;

FIG. 5B is a diagram showing the state where a contact detection pin has been positioned at a wheel diameter measurement position;

FIG. 5C is a diagram showing the state where the wheel diameter is being measured by the contact detection pin;

FIG. 5D is a diagram showing the state where the truing device has been positioned at a truing position for a rotary truer; and

FIG. 5E is a diagram showing the state where truing of the grinding wheel is being performed by the rotary truer.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described below with reference to the accompanying drawings.

A grinding machine of an embodiment of the present invention is a machine tool that grinds a noncircular plate-shaped (e.g., gourd shaped) cam piece (workpiece) that can be attached to a shaft of a camshaft of a vehicle engine. A vertical grinding machine will be described below as an example of the grinding machine of the embodiment with reference to FIGS. 1A to 1E.

As shown in FIGS. 1A and 1B, a grinding machine 1 includes a bed 2, a first headstock 3, a second headstock 4, a wheel spindle stock 5, a discharge device 6, a truing device 7, a moving device 8, a load/unload device 9, and a control device 10 shown in FIG. 1E.

The grinding machine 1 is a machine tool that grinds workpieces W. The first and second headstocks 3, 4 are disposed parallel to each other. The workpieces W are supported by first and second spindle chucks 33, 43 of first and second spindles 31, 41 of the first and second headstocks 3, 4. A grinding wheel 52 is held by a wheel spindle 51 of the wheel spindle stock 5. The grinding machine 1 grounds the workpieces W by moving the grinding wheel 52 between the first and second headstocks 3, 4. The configuration of the grinding machine 1 will be described in detail below. In the following description, the “Z-axis direction (vertical direction)” refers to the axial direction of the wheel spindle 51 of the wheel spindle stock 5 disposed on the bed 2, the “X-axis direction” refers to the lateral direction of a front surface 21 of the bed 2 which is perpendicular to the axial direction of the wheel spindle 51 in a horizontal plane, and the “Y-axis direction” refers to the direction perpendicular to the Z-axis direction and the X-axis direction. The front surface 21 refers to the side of the grinding machine 1 which is shown in FIG. 1B.

As shown in FIGS. 1A and 1B, the bed 2 has the shape of a rectangular prism and is placed on a floor. The first and second headstocks 3, 4, the truing device 7, and the moving device 8 are disposed on the front surface 21 side of the bed 2. The first and second headstocks 3, 4 are placed such that first and second rotation axes L1, L2 of the first and second spindles 31, 41 extend in the Z-axis direction. The truing device 7 performs truing of the grinding wheel 52, and the moving device 8 reciprocates the truing device 7 in the Z-axis direction. The wheel spindle stock 5 and the discharge device 6 are disposed above the bed 2. The wheel spindle stock 5 is placed such that a third rotation axis L3 of the wheel spindle 51 holding the grinding wheel 52 extends in the Z-axis direction. The wheel spindle stock 5 can move in the X-axis direction. The discharge device 6 discharges grinding fluid to the grinding wheel 52. The load/unload device 9 is disposed on the upper part of the front surface 21 of the bed 2. The load/unload device 9 loads and unloads the workpieces W to and from the first and second spindles 31, 41.

As shown in FIGS. 1B and 1C, the first headstock 3 includes the first spindle 31. The first spindle 31 is disposed on the front surface 21 side of the bed 2 and has the first spindle chuck 33 at its upper end. The first spindle 31 rotatably supports the workpiece W by the first spindle chuck 33. The first spindle 31 is supported by the first headstock 3 so that the first spindle 31 can be rotated clockwise as viewed from above in the Z-axis direction by a first spindle drive motor 32. The first spindle drive motor 32 is provided at the lower end of the first headstock 3. Similarly, the second headstock 4 includes the second spindle 41. The second spindle 41 is disposed on the front surface 21 side of the bed 2 and has the second spindle chuck 43 at its upper end. The second spindle 41 rotatably supports the workpiece W by the second spindle chuck 43. The second spindle 41 is supported by the second headstock 4 so that the second spindle 41 can be rotated clockwise as viewed from above in the Z-axis direction by a second spindle drive motor 42. The second spindle drive motor 42 is provided at the lower end of the second headstock 4. The main parts of the first and second headstocks 3, 4 are formed by the first and second spindles 31, 41, and the outermost peripheries of the first and second headstocks 3, 4 match the outermost peripheries of the first and second spindles 31, 41.

The first and second spindles 31, 14 are disposed such that the first and second rotation axes L1, L2 extend in the Z-axis direction and parallel to each other at a predetermined interval in the X-axis direction and that the upper end faces of the first and second spindle chucks 33, 43 are located on the same XY plane m (see FIG. 1B). As shown in FIG. 5A, the first and second spindles 31, 41 are placed so that the distance B between the outer peripheries of the first and second spindles 31, 41 on an XZ plane n (see FIG. 1C) extending through the first and second rotation axes L1, L2 is at least the sum of d and f, where “d” represents the diameter of the grinding wheel 52, and “f” represents the maximum length of the truing device 7 in the X-axis direction (the direction in which the grinding wheel 52 moves). Since the distance B between the outer peripheries of the first and second spindles 31, 41 is at least the sum of d and f, the grinding operation and the truing operation of the grinding wheel 52 can be performed without interference with other members.

As shown in FIGS. 1C and 1D, the wheel spindle stock 5 is provided on the front surface 50 a side of a table 50. The table 50 can be reciprocated in the X-axis direction on a pair of rails 53 by a wheel spindle stock drive motor, not shown. The pair of rails 53 are provided above the bed 2 so as to extend in the X-axis direction. The wheel spindle stock 5 includes the wheel spindle 51. The wheel spindle 51 has a third rotation axis L3, and the third rotation axis L3 extends parallel to the first and second rotation axes L1, L2 and is located on the XZ plane n extending through the first and second rotation axes L1, L2 between the first and second spindles 31, 41. The wheel spindle 51 is supported by the wheel spindle stock 5 so that the wheel spindle 51 can be rotated counterclockwise as viewed from above in the Z-axis direction by a wheel spindle drive motor 54. The wheel spindle drive motor 54 is provided at the upper end of the wheel spindle stock 5.

The wheel spindle 51 moves so that the third rotation axis L3 moves along the XZ plane n extending through the first and second rotation axes L1, L2, that is, the third rotation axis L3 moves in a direction perpendicular to the first and second rotation axes L1, L2. The wheel spindle 51 thus grinds the workpieces W supported by the first and second spindles 31, 41. In order for the wheel spindle 51 to grind the workpieces W in this manner, the grinding wheel 52 is held at the lower end of the wheel spindle 51 so as to be rotatable together with the wheel spindle 51. A grinding point of the workpiece W supported by the first spindle 31 and a grinding point of the workpiece W supported by the second spindle 41 are therefore shifted from each other in a rotation phase direction. If the workpieces have the shape of a circular plate, the grinding point of the workpiece W supported by the first spindle 31 and the grinding point of the workpiece W supported by the second spindle 41 are shifted from each other by 180 degrees in the rotation phase direction. In this example, since the workpieces W have the shape of a noncircular plate, the shift angle between the grinding points varies depending on the rotation phase of the workpieces W.

It is herein assumed that the first spindle 31 is rotated clockwise as viewed from above in the Z-axis direction and the second spindle 41 is rotated counterclockwise as viewed from above in the Z-axis direction. In order to make the relative circumferential speed between the workpiece W and the grinding wheel 52 at the grinding portion the same between the workpieces W, the wheel spindle 51 needs to be rotated counterclockwise as viewed from above in the Z-axis direction when grinding the workpiece W attached to the first spindle 31, and the wheel spindle 51 needs to be rotated clockwise as viewed from above in the Z-axis direction when grinding the workpiece W attached to the second spindle 41. The rotation direction of the wheel spindle 51 therefore needs to be reversed when the wheel spindle 5 s is moved between the first and second spindles 31, 41. Accordingly, rotation control tends to be complicated. If the rotation direction of the wheel spindle 51 is not reversed, grinding conditions vary significantly between the workpiece W attached to the first spindle 31 and the workpiece W attached to the second spindle 41, and the resultant dimensions may vary between the workpieces W.

In the present embodiment, both the first and second spindles 31, 41 are rotated clockwise as viewed above in the Z-axis direction, as described above. The wheel spindle 51 can be rotated in the same direction (in the present embodiment, counterclockwise as viewed from above in the Z-axis direction) regardless of whether the workpiece W attached to the first spindle 31 or the workpiece W attached to the second spindle 41 is to be ground. No reversal of rotation is required, thereby facilitating rotation control.

As shown in FIGS. 1B and 1D, the discharge device 6 is provided on the wheel spindle stock 5 and has first and second nozzles 61, 62. The first and second nozzles 61, 62 can discharge coolant (grinding fluid) during grinding of the workpieces W supported by the first and second spindles 31, 41. The first nozzle 61 needs only to discharge the coolant only when the grinding wheel 52 grinds the workpiece W supported by the first spindle 31, and the second nozzle 62 needs only to discharge the coolant only when the grinding wheel 52 grinds the workpiece W supported by the second spindle 41. This can improve efficiency of coolant supply.

The coolant is supplied from a tank, not shown, to the first and second nozzles 61, 62 via a pump, not shown. The tank is provided in the bed 2. The first and second nozzles 61, 62 are disposed so that the direction in which the coolant is discharged to the workpiece W is different between the workpieces W supported by the first and second spindle chucks 33, 43. Namely, a discharge port of the first nozzle 61 is formed on the left side of the grinding wheel 52 in the X-axis direction so as to discharge the coolant horizontally in the tangential direction to the outer periphery of the grinding wheel 52 as viewed from above in the Z-axis direction. A discharge port of the second nozzle 62 is formed on the right side of the grinding wheel 52 in the X-axis direction so as to discharge the coolant horizontally in the tangential direction to the outer periphery of the grinding wheel 52 as viewed from above in the Z-axis direction.

Specifically, as shown in FIG. 4C, the first spindle 31 rotates clockwise as viewed from above in the Z-axis direction, and the wheel spindle 51 rotates counterclockwise as viewed from above in the Z-axis direction. The coolant is therefore supplied in the direction from top to bottom of the figure. As shown in FIG. 4E, the second spindle 41 rotates clockwise as viewed from above in the Z-axis direction, and the wheel spindle 51 rotates counterclockwise as viewed from above in the Z-axis direction. The coolant is therefore supplied in the direction from bottom to top of the figure.

The direction of the circumferential speed of the grinding wheel 52 at the grinding point of the workpiece W supported by the first spindle 31 is opposite to that of the circumferential speed of the grinding wheel 52 at the grinding point of the workpiece W supported by the second spindle 41. In order to make it easier for the coolant to be introduced into the grinding point, the coolant needs to be supplied from the downstream side of the grinding point in the direction of the circumferential speed. The direction in which the coolant is supplied is therefore changed according to whether the workpiece W supported by the first spindle 31 or the workpiece W supported by the second spindle 41 is to be ground. For example, in the case where the first and second spindles 31, 41 rotate counterclockwise as viewed from above in the Z-axis direction and the wheel spindle 51 rotates clockwise as viewed from above in the Z-axis direction, the coolant is supplied in opposite directions from those shown in FIGS. 4C and 4D.

As shown in FIG. 1B, the truing device 7 is provided on the front surface 21 side of the bed 2 so as to be movable in the Z-axis direction between the first and second spindles 31, 41. The truing device 7 includes a contact detection pin 71 and a rotary truer 72. The contact detection pin 71 is disposed so that the direction in which the contact detection pin 71 moves to measure the outside diameter of the grinding wheel 52 matches the direction in which the wheel spindle 51 moves, and that the measurement point for measuring the outside diameter of the grinding wheel 52 is located on the XZ plane n extending through the first and second rotation axes L1, L2. The rotary truer 72 is located below the contact detection pin 71 in the Z-axis direction, and is positioned so as not to interfere with the contact detection pin 71 when the contact detection pin 71 measures the outside diameter of the grinding wheel 52. The rotary truer 72 is rotationally driven by a truer drive motor 73.

As shown in FIG. 1B, the moving device 8 is provided on the front surface 21 side of the bed 2 and is located below the truing device 7 in the Z-axis direction. The moving device 8 includes a truing device drive motor 81 and a ball screw mechanism 82. A ball screw of the ball screw mechanism 82 is coupled to the truing device drive motor 81, and a nut of the ball screw mechanism 82 is fixed to the truing device 7. The moving device 8 is driven by the truing device drive motor 81 to reciprocate the truing device 7 in the Z-axis direction.

As shown in FIGS. 1B and 1C, the load/unload device 9 includes first and second robots 91, 92. The first and second robots 91, 92 are provided at the upper ends of two L-shaped brackets 22, 22 disposed on both sides of the front surface 21 of the bed 2. The first robot 91 includes a first arm 93, a first holding device 94, and a first arm drive motor 95. The first arm 93 has a substantially U-shape as viewed from above in the Z-axis direction. The first holding device 94 is provided at one end of the first arm 93, and the first arm drive motor 95 is provided at the other end of the first arm 93. Similarly, the second robot 92 includes a second arm 96, a second holding device 97, and a second arm drive motor 98. A conveyor 99 (see FIG. 3A) that carries the workpieces W is provided below the load/unload device 9 so as to extend in the X-axis direction.

As shown in FIG. 1B, a first robot chuck 94 a and a second robot chuck 94 b are arranged next to each other in the first holding device 94. The first robot chuck 94 a picks up a workpiece W from the conveyor 99 at its lower end, and sets the workpiece W on the first spindle chuck 33. The second robot chuck 94 b picks up the workpiece W from the first spindle 31 at its lower end, and sets the workpiece W on the conveyor 99. Similarly, a first robot chuck 97 a and a second robot chuck 97 b are arranged next to each other in the second holding device 97.

The other end of the first arm 93 is rotatably supported by the upper end of the bracket 22, and the first arm 93 is driven by the first arm drive motor 95 to rotate back and forth between the conveyor 99 and the first spindle chuck 33. The first robot chuck 94 a and the second robot chuck 94 b are disposed on the circumference k of the rotation of the first arm 93 (see FIG. 3A), and are positioned at a workpiece pickup position and a workpiece set position by the rotation of the first arm 93. The second arm 96, the first robot chuck 97 a, and the second robot chuck 97 b are configured similarly.

As described in detail below, the control device 10 controls loading and unloading of the workpieces W to and from the grinding machine 1, controls grinding of the workpiece W, and controls truing of the grinding wheel 52 as necessary.

As shown in FIG. 1E, the control device 10 includes a first spindle control unit 101, a second spindle control unit 102, a wheel spindle control unit 103, a wheel spindle stock control unit 104, a first nozzle control unit 105, a second nozzle control unit 106, a truing device control unit 107, a first robot control unit 108, a second robot control unit 109, a machining start phase adjusting unit 110, and a load/unload command unit 111.

The first spindle control unit 101 drivingly controls a chuck motor, not shown, to open or close a jaw of the first spindle chuck 33 to support or release the workpiece W. The first spindle control unit 101 drivingly controls the first spindle drive motor 32 to rotate the first spindle 31 to rotate the workpiece W supported by the first spindle chuck 33.

The second spindle control unit 102 drivingly controls a chuck motor, not shown, to open or close a jaw of the second spindle chuck 43 to support or release the workpiece W.

The second spindle control unit 102 drivingly controls the second spindle drive motor 42 to rotate the second spindle 41 to rotate the workpiece W supported by the second spindle chuck 43.

The wheel spindle control unit 103 drivingly controls the wheel spindle drive motor 54 to rotate the wheel spindle 51 to rotate the grinding wheel 52 held by the wheel spindle 51.

The wheel spindle stock control unit 104 drivingly controls a wheel spindle stock drive motor, not shown, to move the wheel spindle stock 5 in the X-axis direction.

The first nozzle control unit 105 drivingly controls the pump, not shown, to discharge the coolant from the first nozzle 61.

The second nozzle control unit 106 drivingly controls the pump, not shown, to discharge the coolant from the second nozzle 62.

The truing device control unit 107 drivingly controls the truing device drive motor 81 to move the truing device 7 in the Z-axis direction. The truing device control unit 107 also controls the truer drive motor 73 to rotate the truer 72.

The first robot control unit 108 drivingly controls a chuck motor, not shown, to open or close jaws of the first and second robot chucks 94 a, 94 b to pick up or set the workpiece W. The first robot control unit 108 also drivingly controls the first arm drive motor 95 to rotate the first arm 93 to move the workpieces W supported by the first and second robot chucks 94 a, 94 b.

The second robot control unit 109 drivingly controls a chuck motor, not shown, to open or close jaws of the first and second robot chucks 97 a, 97 b to pick up or set the workpiece W. The second robot control unit 109 also drivingly controls the second arm drive motor 98 to rotate the second arm 96 to move the workpieces W supported by the first and second robot chucks 97 a, 97 b.

The machining start phase adjusting unit 110 sends the second spindle control unit 102 or the first spindle control unit 101 a command to adjust the workpiece W supported by the second spindle chuck 43 of the second spindle 41 or the workpiece W supported by the first spindle chuck 33 of the first spindle 31 to a predetermined machining start phase. The machining start phase adjusting unit 110 sends this command during grinding of the workpiece W supported by the first spindle chuck 33 of the first spindle 31 or during grinding of the workpiece W supported by the second spindle chuck 43 of the second spindle 41, or while the wheel spindle 51 is moving from the first headstock 3 toward the second headstock 4 or while the wheel spindle 51 is moving from the second headstock 4 toward the first headstock 3. Adjustment of the machining start phase is required particularly when the workpieces W have a noncircular shape.

The load/unload command unit 111 sends the second robot control unit 109 or the first robot control unit 108 a command to unload the workpiece W from the second spindle chuck 43 of the second spindle 41 and load a new workpiece W onto the second spindle chuck 43 or a command to unload the workpiece W from the first spindle chuck 33 of the first spindle 31 or load a new workpiece W onto the first spindle chuck 33. The load/unload command unit 111 sends this command during grinding of the workpiece W supported by the first spindle chuck 33 of the first spindle 31 or the second spindle chuck 43 of the second spindle 41.

Operation of the load/unload device 9 etc. will be described with reference to the operation diagrams of FIGS. 3A to 3D. Operation of the first robot 91 is different from that of the second robot 92 only in the rotational direction of the first arm 93 and the second arm 96 at the time of loading the workpiece W. That is, the first arm 93 rotates counterclockwise as viewed from above in the Z-axis direction to load the workpiece W, whereas the second arm 96 rotates clockwise as viewed from above in the Z-axis direction to load the workpiece W. Accordingly, only operation of the first arm 93 will be described below. It is herein assumed that the workpiece W that has already been ground is supported on the first spindle chuck 33 of the first spindle 31. The original position of the first arm 93 is such a position that the first robot chuck 94 a can pick up the workpiece W carried on the conveyor 99.

The first robot control unit 108 checks if the first arm 93 has been positioned at the original position and a workpiece W has been carried to the load position on the conveyor 99. If the first arm 93 has been positioned at the original position and a workpiece W has been carried to the load position on the conveyor 99, the first robot control unit 108 drivingly controls the chuck motor to close the jaw of the first robot chuck 97 a of the first arm 93 to pick up the workpiece W to be ground (see FIG. 3A).

The first robot control unit 108 drivingly controls the first arm drive motor 95 to rotate the first arm 93 counterclockwise to position the second robot chuck 97 b of the first arm 93 on the first spindle chuck 33 of the first spindle 31. The first robot control unit 108 drivingly controls the chuck motor to close the jaw of the second robot chuck 97 b of the first arm 93 to pick up the workpiece W that has been ground from the first spindle chuck 33 of the first spindle 31 (see FIG. 3B).

The first robot control unit 108 drivingly controls the first arm drive motor 95 to rotate the first arm 93 counterclockwise to position the first robot chuck 97 a of the first arm 93 on the first spindle chuck 33 of the first spindle 31. The first robot control unit 108 drivingly controls the chuck motor to open the jaw of the first robot chuck 97 a of the first arm 93 to set the workpiece W to be ground onto the first spindle chuck 33 of the first spindle 31 (see FIG. 3C).

The first robot control unit 108 drivingly controls the first arm drive motor 95 to rotate the first arm 93 clockwise to position the second robot chuck 97 b of the first arm 93 at the unload position on the conveyor 99. The first robot control unit 108 drivingly controls the chuck motor to open the jaw of the second robot chuck 97 b of the first arm 93 to set the workpiece W that has been ground at the unload position on the conveyor 99 (see FIG. 3D). The above operation is repeated until all the workpieces W to be ground on the first spindle 31 are ground.

Operation of the first and second headstocks 3, 4, the wheel spindle stock 5, the discharge device 6, etc. will be described with reference to the operation diagrams of FIGS. 4A to 4E.

When a workpiece W to be ground is received from the first robot 91, the first spindle control unit 101 drivingly controls the chuck motor to close the jaw of the first spindle chuck 33 of the first spindle 31 to support the workpiece W. The machining start phase adjusting unit 110 adjusts the workpiece W supported by the first spindle chuck 33 to a preset machining start phase (see FIG. 4A). The wheel spindle stock control unit 104 drivingly controls the wheel spindle stock drive motor to move the wheel spindle stock 5 to the left in the X-axis direction to position the grinding wheel 52 at a grinding start position for the workpiece W on the first spindle chuck 33 (see FIG. 4B).

The wheel spindle control unit 103 drivingly controls the wheel spindle drive motor 54 to rotate the wheel spindle 51 counterclockwise to rotate the grinding wheel 52 held by the wheel spindle 51. The first nozzle control unit 105 drivingly controls the pump to discharge the coolant from the first nozzle 61. The first spindle control unit 101 drivingly controls the first spindle drive motor 32 to rotate the first spindle 31 clockwise to rotate the workpiece W on the first spindle chuck 33 clockwise. The wheel spindle stock control unit 104 drivingly controls the wheel spindle stock drive motor to move the wheel spindle stock 5 in the X-axis direction to bring the grinding wheel 52 into contact with the workpiece W on the first spindle chuck 33, thereby grinding the workpiece W on the first spindle chuck 33 (see FIG. 4C).

During grinding of the workpiece W on the first spindle chuck 33, the load/unload command unit 111 sends the second robot control unit 109 a command to load a new workpiece W to be supported by the second spindle chuck 43 of the second spindle 41. The second robot control unit 109 picks up the new workpiece W from the conveyor 99 by the second robot 92 and sets the new workpiece W onto the second spindle chuck 43. When the workpiece W to be ground is received from the second robot 92, the second spindle control unit 102 drivingly controls the chuck motor to close the jaw of the second spindle chuck 43 to support the workpiece W. During grinding of the workpiece W on the first spindle chuck 33, the machining start phase adjusting unit 110 adjusts the workpiece W on the second spindle chuck 43 to a preset machining start phase (see FIG. 4C).

When grinding of the workpiece W on the first spindle chuck 33 is completed, the first spindle control unit 101 drivingly controls the first spindle drive motor 32 to stop rotation of the first spindle 31. The first nozzle control unit 105 drivingly controls the pump to stop discharge of the coolant from the first nozzle 61. The wheel spindle stock control unit 104 drivingly controls the wheel spindle stock drive motor to move the wheel spindle stock 5 to the right in the X-axis direction to position the grinding wheel 52 at a grinding start position for the workpiece W on the second spindle chuck 43 (see FIG. 4D).

The second nozzle control unit 106 drivingly controls the pump to discharge the coolant from the second nozzle 62. The second spindle control unit 102 drivingly controls the second spindle drive motor 42 to rotate the second spindle 41 clockwise to rotate the workpiece W on the second spindle chuck 43 clockwise. The wheel spindle stock control unit 104 drivingly controls the wheel spindle stock drive motor to move the wheel spindle stock 5 in the X-axis direction to bring the grinding wheel 52 into contact with the workpiece W on the second spindle chuck 43, thereby grinding the workpiece W on second spindle chuck 43.

During grinding the workpiece on the second spindle chuck 43, the load/unload command unit 111 sends the first robot control unit 108 a command to load a new workpiece W to be supported by the first spindle chuck 33. The first robot control unit 108 picks up the new workpiece W from the conveyor 99 by the first robot 91 and sets the new workpiece W onto the first spindle chuck 33. If the workpiece W to be ground is received from the first robot 91, the first spindle control unit 101 drivingly controls the chuck motor to close the jaw of the first spindle chuck 33 to support the workpiece W. The machining start phase adjusting unit 110 adjusts the workpiece W on the first spindle chuck 33 to a preset machining start phase during grinding of the workpiece W on the second spindle chuck 43. The above operation is alternately repeated until all the workpieces W to be ground on the first spindle 31 and the second spindle 41 are ground.

Operation of the truing device 7, the moving device 8, the wheel spindle stock 5, etc. will be described below with reference to the operation diagrams of FIGS. 5A to 5E. When not in use, the truing device 7 is located at such a predetermined standby position below the grinding wheel 52 that the truing device 7 does not interfere with movement of the grinding wheel 52 in the X-axis direction (see FIG. 5A).

The truing device control unit 107 drivingly controls the truing device drive motor 81 to move the truing device 7 upward in the Z-axis direction from the standby position to position the truing device 7 at a predetermined wheel diameter measurement position for the contact detection pin 71 (see FIG. 5B). The wheel spindle stock control unit 104 drivingly controls the wheel spindle stock drive motor to move the wheel spindle stock 5 in the X-axis direction to move the grinding wheel 52 toward the contact detection pin 71. If AE waves of an AE sensor S become larger than a prestored predetermined threshold signal level, the truing device control unit 107 determines that the grinding wheel 52 has contacted the contact detection pin 71, and stores the position of the grinding wheel 52 contacting the contact detection pin 71 (see FIG. 5C).

The truing device control unit 107 moves the truing device 7 upward in the Z-axis direction from the wheel diameter measurement position to position the truing device 7 at a predetermined truing position for the rotary truer 72 (see FIG. 5D). The wheel spindle control unit 103 drivingly controls the wheel spindle drive motor 54 to rotate the wheel spindle 51 to rotate the grinding wheel 52 held by the wheel spindle 51, and the truing device control unit 107 controls the truer drive motor 73 to rotate the rotary truer 72. The wheel spindle stock control unit 104 moves the wheel spindle stock 5 in the X-axis direction to bring the grinding wheel 52 into contact with the rotary truer 72, and the truing device control unit 107 moves the truing device 7 in the Z-axis direction to perform truing (see FIG. 5E).

After the truing is completed, the wheel spindle control unit 103 stops rotation of the grinding wheel 52, and the truing device control unit 107 stops rotation of the rotary truer 72. The wheel spindle stock control unit 104 moves the wheel spindle stock 5 in the X-axis direction to separate the grinding wheel 52 from the rotary truer 72. The truing device control unit 107 moves the truing device 7 downward in the Z-axis direction from the truing position to position the truing device 7 at the wheel diameter measurement position. The wheel spindle stock control unit 104 rotates the grinding wheel 52 and moves the wheel spindle stock 5 in the X-axis direction to bring the grinding wheel 52 into contact with the contact detection pin 71. The wheel spindle stock control unit 104 thus stores the position of the grinding wheel 52 after the truing, and updates data on the grinding wheel 52 by using the difference between the wheel diameters of the grinding wheel 52 measured before and after the truing as a decrease in wheel diameter due to the truing.

A series of operations of the grinding machine 1 that is controlled by the control device 10 will be described with reference to the timing chart of FIG. 2. This example will be described with respect to the case where the subsequent operation is started after one operation is completed for each of the first spindle 31 and the second spindle 41. However, the subsequent operation may be started during the one operation if problems such as interference between members do not occur.

First, at time t1, the control device 10 operates the first robot 91 to start loading of the workpiece W onto the first spindle 31. At time t2, if it is determined that loading of the workpiece W onto the first spindle 31 has been completed, the control device 10 moves the grinding wheel 52 toward the first headstock 3.

At time t3, if it is determined that the grinding wheel 52 has been positioned at the grinding start position on the first headstock 3 side, the control device 10 rotates the grinding wheel 52 and the first spindle 31 to start grinding of the workpiece W on the first spindle 31. At the same time, the control device 10 operates the second robot 92 to start loading of the workpiece W onto the second spindle 41. At time t4, if it is determined that loading of the workpiece W onto the second spindle 41 has been completed, the control device 10 suspends operation on the second spindle 41 side and continues grinding of the workpiece W on the first spindle 31.

At time t5, if it is determined that grinding of the workpiece W on the first spindle 31 has been completed, the control device 10 moves the grinding wheel 52 toward the second headstock 4. At time t6, if it is determined that the grinding wheel 52 has been positioned at the grinding start position on the second headstock 4 side, the control device 10 rotates the second spindle 41 to start grinding of the workpiece W on the second spindle 41. At the same time, the control device 10 operates the first robot 91 to start unloading of the workpiece W that has been ground from the first spindle 31 and loading of a new workpiece W onto the first spindle 31.

At time t7, if it is determined that unloading of the workpiece W that has been ground from the first spindle 31 and loading of the new workpiece W onto the first spindle 31, the control device 10 suspends operation on the first spindle 31 side and continues grinding of the workpiece W on the second spindle 41. At time t8, if it is determined that grinding of the workpiece Won the second spindle 41 has been completed, the control device 10 moves the grinding wheel 52 toward the first headstock 3.

At time t9, if it is determined that the grinding wheel 52 has been positioned at the grinding start position on the first headstock 3 side, the control device 10 rotates the first spindle 31 to start grinding of the workpiece W on the first spindle 31. At the same time, the control device 10 operates the second robot 92 to start unloading of the workpiece W that has been ground from the second spindle 41 and loading of a new workpiece W onto the second spindle 41. The above operation is repeated until all the workpieces W to be ground on the first spindle 31 and the second spindle 41 are ground.

The grinding machine 1 of the present embodiment includes the first headstock 3, the second headstock 4, the wheel spindle stock 5, the wheel spindle 51, and the grinding wheel 52. The first headstock 3 has the first spindle 31 that can rotate about the first rotation axis L1 extending in the vertical direction and that rotatably supports a workpiece (first workpiece) W. The second headstock 4 has the second spindle 41 that can rotate about the second rotation axis L2 separated from the first rotation axis L1 at a predetermined interval and extending parallel to the first rotation axis L1, and that rotatably supports a workpiece (second workpiece) W different from the first workpiece W. The wheel spindle stock 5 has the third rotation axis L3 extending parallel to the first and second rotation axes L1, L2, and moves between the first and second headstocks 3, 4 so that the third rotation axis L3 moves in the direction perpendicular to the first and second rotation axes L1, L2 on the XZ plane n extending through the first and second rotation axes L1, L2. The wheel spindle 51 is rotatably provided in the wheel spindle stock 5. The grinding wheel 52 is provided on the wheel spindle 51. The grinding wheel 52 grinds the first workpiece W as the wheel spindle stock 5 moves toward the first headstock 3, and grinds the second workpiece W as the wheel spindle stock 5 moves toward the second headstock 4.

The direction in which the grinding wheel 52 moves between the first and second headstocks 3, 4 is the same as the direction in which the grinding wheel 52 grinds the first and second workpieces W supported on the first and second spindles 31, 41 when grinding the first and second workpieces W. This eliminates the need for a grinding moving mechanism separate from the inter-spindle moving mechanism, which simplifies the device configuration and reduces facility cost.

The control device 10 controls grinding of the workpiece W so that the grinding wheel 52 rotates in the same direction both when grinding the workpiece W supported on the first spindle 31 and when grinding the workpiece W supported on the second spindle 41. Due to the positional relationship between the grinding wheel 52 and the first and second spindles 31, 41, the grinding point of the grinding wheel 52 at the time of grinding the workpiece supported on the first spindle 31 is shifted in the rotation phase direction from the grinding point of the grinding wheel 52 at the time of grinding the workpiece W supported on the second spindle 41. This configuration eliminates the need to control the rotational direction of the grinding wheel 52. Moreover, this configuration can significantly improve machining efficiency as the workpieces W on the first and second spindles 31, 41 can be continuously ground without stopping driving of the first and second spindles 31, 41.

The truing device 7 is disposed between the first and second headstocks 3, 4 so that the direction in which the truing device 7 moves to measure the outside diameter of the grinding wheel 52 matches the direction in which the wheel spindle 51 moves, and that the measurement point for measuring the outside diameter of the grinding wheel 52 is located on the XZ plane n extending through the first and second rotation axes L1, L2. Since truing of the grinding wheel 52 can be performed in the same direction as the grinding direction, truing efficiency can be significantly improved.

The main parts of the first and second headstocks 3, 4 are formed by the first and second spindles 31, 41, and the outermost peripheries of the first and second headstocks 3, 4 match the outermost peripheries of the first and second spindles 31, 41. The first and second spindles 31, 41 are placed so that the distance B between the outer peripheries of the first and second spindles 31, 41 on the XZ plane n extending through the first and second rotation axes L1, L2 is at least the sum of d and f, where “d” represents the diameter of the grinding wheel 52, and “f” represents the maximum length of the truing device 7 in the direction in which the grinding wheel 52 moves. Since the distance B between the outer peripheries of the first and second spindles 31, 41 is at least the sum of d and f, the grinding operation and the truing operation of the grinding wheel 52 can be performed without interference with other members.

The grinding machine 1 includes the moving device 8 that moves the truing device 7 in the vertical direction. The grinding machine 1 grinds noncircular workpieces W. Grinding resistance is higher in the case of grinding noncircular workpieces W than in the case of grinding circular workpieces W. It is therefore necessary to increase rigidity of the wheel spindle 51. Since the truing device 7 can be moved in the Z-axis direction by the moving device 8, the wheel spindle 51 need not be provided with a moving device for movement in the Z-axis direction. Rigidity of the wheel spindle 51 is therefore not reduced by the Z-axis moving device. Accordingly, the rigidity of the wheel spindle 51 can be increased as compared to the case where the wheel spindle 51 is provided with the Z-axis moving device. Grinding accuracy of the noncircular workpieces W can thus be increased.

The control device 10 includes the machining start phase adjusting unit 110 that adjusts the workpiece W supported by the second spindle 41 to the preset machining start phase during grinding of the workpiece W supported by the first spindle 31 or while the wheel spindle 51 is moving from the first headstock 3 toward the second headstock 4. This reduces the grinding time of the grinding machine 1 as compared to the case of grinding the workpieces W one by one. Machining efficiency can therefore be improved.

The grinding machine 1 includes the load/unload device 9 that can load and unload the workpiece W to and from the first and the second spindles 31, 41. The control device 10 includes the load/unload command unit 111 that sends a command to unload the workpiece W supported by the second spindle 41 or the first spindle 31 and load a new workpiece W onto the second spindle 41 or the first spindle 31 to the load/unload device 9 during grinding of the workpiece W supported by the first spindle 31 or the second spindle 41. This reduces the grinding time of the grinding machine 1 as compared to the case of grinding the workpieces W one by one. Machining efficiency can therefore be improved.

The grinding machine 1 includes the discharge device 6 having the two nozzles, namely the first and second nozzles 61, 62, which can discharge the coolant during grinding of the workpieces W supported by the first and second spindles 31, 41. Discharge of the coolant from the second nozzle 62 or the first nozzle 61 can be stopped when the first nozzle 61 or the second nozzle 62 is discharging the coolant. This can save energy.

The first and second nozzles 61, 62 are placed so that the direction in which the grinding fluid is discharged to the workpieces W supported by the first and the second spindles 31, 41 is the same as the direction of the circumferential speed of the grinding wheel 52 at the grinding point of the first or second workpiece W. The direction of the circumferential speed of the grinding wheel 52 at the grinding point of the workpiece W supported by the first spindle 31 is different from that of the circumferential speed of the grinding wheel 52 at the grinding point of the workpiece W supported by the second spindle 41. Accordingly, if the coolant is supplied in the same direction to the first and second workpieces W, the coolant is easily supplied to the grinding point of one of the first and second workpieces W as it is supplied along the rotation. However, the coolant is less likely to be supplied to the grinding point of the other workpiece W as the coolant is supplied in the opposite direction to the direction of the rotation. Since the first and second nozzles 61, 62 are arranged so as to discharge the coolant in different directions from each other, the coolant is reliably supplied to the workpieces W supported by the first and second spindles 31, 41, and defects such as grinding burn can be prevented.

In the above embodiment, the workpiece W on the first spindle chuck 33 or the second spindle chuck 43 is adjusted to the machining start phase during grinding of the workpiece W on the second spindle chuck 43 or the first spindle chuck 33. However, this adjustment may be made while the grinding wheel 52 is being moved toward the first headstock 3 or the second headstock 4 after grinding of the workpiece W on the second spindle chuck 43 or the first spindle chuck 33.

In the above embodiment, the grinding machine 1 includes the moving device 8 that moves the truing device 7 in the Z-axis direction. However, the grinding machine 1 may not include the moving device 8, and may include a device that moves the wheel spindle 51 in the Z-axis direction. Such a grinding machine 1 can perform not only external grinding by internal chucking but also internal grinding by external chucking.

In the above embodiment, the first and second spindles 31, 41 are rotated clockwise as viewed from above in the Z-axis direction, and the grinding wheel 52 is rotated counterclockwise as viewed from above in the Z-axis direction. However, the first and second spindles 31, 41 may be rotated counterclockwise as viewed from above in the Z-axis direction, and the grinding wheel 52 may be rotated clockwise as viewed from above in the Z-axis direction. Alternatively, the first spindle 31 may be rotated clockwise as viewed from above in the Z-axis direction, the second spindle 41 may be rotated counterclockwise as viewed from above in the Z-axis direction, and the grinding wheel 52 may be rotated counterclockwise for the first spindle 31 as viewed from above in the Z-axis direction and may be rotated clockwise for the second spindle 41 as viewed from above in the Z-axis direction.

The above embodiment is described with respect to the case where the present invention is applied to the vertical grinding machine. However, the present invention is similarly applicable to a horizontal grinding machine. 

What is claimed is:
 1. A grinding machine, comprising: a first headstock having a first spindle that can rotate about a first rotation axis extending in a vertical direction and that rotatably supports a first workpiece; a second headstock having a second spindle that can rotate about a second rotation axis separated from the first rotation axis at a predetermined interval and extending parallel to the first rotation axis, and that rotatably supports a second workpiece different from the first workpiece; a wheel spindle stock that has a third rotation axis extending parallel to the first and second rotation axes and that moves between the first and second headstocks so that the third rotation axis moves in a direction perpendicular to the first and second rotation axes on a plane extending through the first and second rotation axes; a wheel spindle that is rotatably provided in the wheel spindle stock; and a grinding wheel that is provided on the wheel spindle, that grinds the first workpiece as the wheel spindle stock moves toward the first headstock, and that grinds the second workpiece as the wheel spindle stock moves toward the second headstock.
 2. The grinding machine according to claim 1, further comprising: a control device that controls grinding of the workpieces; wherein the control device controls the grinding of the workpieces so that the grinding wheel rotates in the same direction both when grinding the first workpiece and when grinding the second workpiece.
 3. The grinding machine according to claim 1, further comprising: a truing device that performs truing of the grinding wheel; wherein the truing device is disposed between the first and second headstocks so that a direction in which the truing device moves to measure an outside diameter of the grinding wheel matches a direction in which the wheel spindle stock moves, and that a measurement point for measuring the outside diameter of the grinding wheel is located on the plane extending through the first and second rotation axes.
 4. The grinding machine according to claim 2, further comprising: a truing device that performs truing of the grinding wheel; wherein the truing device is disposed between the first and second headstocks so that a direction in which the truing device moves to measure an outside diameter of the grinding wheel matches a direction in which the wheel spindle stock moves, and that a measurement point for measuring the outside diameter of the grinding wheel is located on the plane extending through the first and second rotation axes.
 5. The grinding machine according to claim 3, wherein the first and second headstocks are placed so that a distance between outer peripheries of the first and second headstocks on the plane extending through the first and second rotation axes is at least a sum of a diameter of the grinding wheel and a maximum length of the truing device in the direction in which the wheel spindle stock moves.
 6. The grinding machine according to claim 4, wherein the first and second headstocks are placed so that a distance between outer peripheries of the first and second headstocks on the plane extending through the first and second rotation axes is at least a sum of a diameter of the grinding wheel and a maximum length of the truing device in the direction in which the wheel spindle stock moves.
 7. The grinding machine according to claim 3, further comprising: a moving device that moves the truing device in the vertical direction; wherein the grinding machine grinds the workpieces each having a noncircular shape.
 8. The grinding machine according to claim 2, wherein the control device includes an adjusting unit that adjusts the second workpiece to a preset machining start phase during grinding of the first workpiece or while the wheel spindle is moving from the first headstock toward the second headstock.
 9. The grinding machine according to claim 2, further comprising: a load/unload device that can load and unload the workpieces to and from the first and the second spindles; wherein the control device includes a command unit that sends a command to unload the second workpiece or the first workpiece and load a new workpiece onto the second workpiece or the first workpiece to the load/unload device during grinding of the first workpiece or the second workpiece.
 10. The grinding machine according to claim 1, further comprising: a discharge device having two nozzles that can discharge grinding fluid during grinding of the first or second workpiece.
 11. The grinding machine according to claim 10, wherein the two nozzles are placed so that a direction in which the grinding fluid is discharged to the first or second workpiece is the same as a direction of a circumferential speed of the grinding wheel at a grinding point of the first or second workpiece.
 12. A grinding method for grinding the workpieces by the grinding machine according to claim 1, comprising: grinding the workpieces by controlling the grinding machine so that the first and second workpieces rotate in the same direction and the grinding wheel and the workpieces rotate in opposite directions. 